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    1   /*
    2    * Copyright (c) 1997, 2010, Oracle and/or its affiliates. All rights reserved.
    3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
    4    *
    5    * This code is free software; you can redistribute it and/or modify it
    6    * under the terms of the GNU General Public License version 2 only, as
    7    * published by the Free Software Foundation.  Oracle designates this
    8    * particular file as subject to the "Classpath" exception as provided
    9    * by Oracle in the LICENSE file that accompanied this code.
   10    *
   11    * This code is distributed in the hope that it will be useful, but WITHOUT
   12    * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   13    * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   14    * version 2 for more details (a copy is included in the LICENSE file that
   15    * accompanied this code).
   16    *
   17    * You should have received a copy of the GNU General Public License version
   18    * 2 along with this work; if not, write to the Free Software Foundation,
   19    * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   20    *
   21    * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   22    * or visit www.oracle.com if you need additional information or have any
   23    * questions.
   24    */
   25   
   26   package java.util;
   27   
   28   /**
   29    * An iterator over a collection.  {@code Iterator} takes the place of
   30    * {@link Enumeration} in the Java Collections Framework.  Iterators
   31    * differ from enumerations in two ways:
   32    *
   33    * <ul>
   34    *      <li> Iterators allow the caller to remove elements from the
   35    *           underlying collection during the iteration with well-defined
   36    *           semantics.
   37    *      <li> Method names have been improved.
   38    * </ul>
   39    *
   40    * <p>This interface is a member of the
   41    * <a href="{@docRoot}/../technotes/guides/collections/index.html">
   42    * Java Collections Framework</a>.
   43    *
   44    * @param <E> the type of elements returned by this iterator
   45    *
   46    * @author  Josh Bloch
   47    * @see Collection
   48    * @see ListIterator
   49    * @see Iterable
   50    * @since 1.2
   51    */
   52   public interface Iterator<E> {
   53       /**
   54        * Returns {@code true} if the iteration has more elements.
   55        * (In other words, returns {@code true} if {@link #next} would
   56        * return an element rather than throwing an exception.)
   57        *
   58        * @return {@code true} if the iteration has more elements
   59        */
   60       boolean hasNext();
   61   
   62       /**
   63        * Returns the next element in the iteration.
   64        *
   65        * @return the next element in the iteration
   66        * @throws NoSuchElementException if the iteration has no more elements
   67        */
   68       E next();
   69   
   70       /**
   71        * Removes from the underlying collection the last element returned
   72        * by this iterator (optional operation).  This method can be called
   73        * only once per call to {@link #next}.  The behavior of an iterator
   74        * is unspecified if the underlying collection is modified while the
   75        * iteration is in progress in any way other than by calling this
   76        * method.
   77        *
   78        * @throws UnsupportedOperationException if the {@code remove}
   79        *         operation is not supported by this iterator
   80        *
   81        * @throws IllegalStateException if the {@code next} method has not
   82        *         yet been called, or the {@code remove} method has already
   83        *         been called after the last call to the {@code next}
   84        *         method
   85        */
   86       void remove();
   87   }

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